Router Bit Toast or What?

[Derek Arita]

So I just burnt the crap out of my 3/8" carbide upcut bit, cutting a bunch of slots in some MDF, which I know can be tuff on bits. This bit was only used a few times. Question is, did I destroy it, is it cleanable, does it need to be resharpened or what? There is char on the bit that I couldn't just wipe off.
https://i.imgur.com/iG8NxC6.jpg

[Kevin Jenness]

Clean off the schmutz with blade cleaner, lye or whathaveyou and a brush, then test it for sharpness by dragging a fingernail across it. A dull edge will skate across the nail, a sharp edge will catch and dig in. I have had carbide spirals sharpened by CT Saw and Vortex.

You can minimize burning with lower rpms and a faster feed rate. This will increase the chip load and transfer more of the heat away from the bit.

[Richard Coers]

3/8" carbide upcut bit
Sure looks like a down cut spiral to me! The main reason I don't like down cut and MDF. That kind of heat, and the abrasive nature of MDF has probably degraded the edge a little. Resharpen time in my opinion.

[Zachary Hoyt]

I always figure with steel tools that if it got hot enough to change color it's dead, but I don't know if that applies to carbide.

[Lee Schierer]

How deep were the cuts you were doing with this bit? If the chips can't get clear of the cut, the result is heat and that can lead to bits like the one you have and it may also leave nasty burn marks on your work piece that are near impossible to remove. The fact that the shaft that would have been in the collet is also blue would indicate you had this bit really hot.
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[Mel Fulks]

I always figure with steel tools that if it got hot enough to change color it's dead, but I don't know if that applies to carbide.

If it’s real high-speed steel some heat won’t hurt it ,even if it gets a little burnt looking. I don’t you are likely to hurt carbide with heat .

[Richard Coers]

How deep were the cuts you were doing with this bit? If the chips can't get clear of the cut, the result is heat and that can lead to bits like the one you have and it may also leave nasty burn marks on your work piece that are near impossible to remove. The fact that the shaft that would have been in the collet is also blue would indicate you had this bit really hot.
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It didn't clear the chips because it's a down spiral.

[John Lanciani]

It didn't clear the chips because it's a down spiral.

Only if its a backwards rotation (CCW) bit. Look closer, thats an upspiral.

[Richard Coers]

Only if its a backwards rotation (CCW) bit. Look closer, thats an upspiral.
Well, that sure is embarrassing, my mistake, sorry! Senior moment I guess.

[Jerome Stanek]

Moving to slow when cutting feed rate needs to be pretty fast. You want the chips to be hot not the bit

[Derek Arita]

I was taking 1/4" deep cuts, down to 3/4" total. For MDF, where should my cutter speed be 1-6?

[Kevin Jenness]

It depends on your bit diameter, # of flutes, feed rate and available power. Look up a chip load table to get an idea of the ideal balance, then experiment. Since you are not posting in the cnc forum I assume you are using a hand held router with speeds ranging in the 10-22,000 rpm range. It looks like you have a 1/2" diameter bit. I'd probably use an intermediate rpm like 16,000 and push it as fast as feels comfortable, like 15 or 20 feet/min. Experiment.

It's easier to dial it in with a cnc machine. A general method is to try out a rotational speed, then increase the feed rate until cut quality suffers (some people say until you start breaking bits but that seems a bit extreme to me). With low power on the spindle or feed motors you may not be able to hit the ideal rate, so a shallower cut may be necessary.

Heat is the enemy of sharpness. You aren't likely to destroy a carbide bit but you can certainly severely dull it by running it for too long with too low a rate of stock removal.

[Charles Coolidge]

The last time I did that to a carbide bit I was running it backwards. I carried on a bit even with the workpiece smoking and trying to catch on fire.

[Bill Dufour]

A shop that sharpens endmills for metal working can also do wood workers router bits. Make sure they know it is for cutting wood so they use the correct relief angles.
Bill D